Cymbals have traditionally been an acoustic-only instrument. For live performance in large spaces or recording sessions, microphones are commonly used to pick up the cymbal sound for subsequent amplification and/or recording, but the desire is to remain faithful to the natural sound of the cymbals. Occasionally, a moderate post-processing effect such as reverb or equalization is applied to tailor the sound of the cymbal as required or desired.
The advent of electronic drum kits has naturally given rise to “electronic cymbals.” Like their drum counterparts, these devices are used as electronic “triggers,”—that is, the sound of the “cymbal” itself being struck is not amplified for listening or intended to be heard at all. The prior art “cymbal” (or more accurately, a plastic or plastic-covered replica of a cymbal) of this type is fabricated with an impact sensor, producing trigger signals that initiate playback of pre-recorded or canned “samples” of acoustic cymbal sounds when struck. The “sound” of the electronic cymbal is changed by changing the sample(s) that are triggered by the sensor being struck. While this approach offers advantages of virtually silent operation and “authentic” pre-recorded cymbal sounds, it suffers greatly in “feel” and “expression.” Drummers are accustomed to the feel of “stick-on-metal” that a traditional metal acoustic cymbal provides, and the very large range of sound variation achievable by striking an acoustic cymbal in different locations with varying types of strikes, strike force, and striking objects (sticks, mallets, brushes, etc.). Practical, cost-effective sample-triggering schemes are not available for providing the feel and range of expression that drummers are accustomed to with acoustic cymbals.
When, alternatively, a conventional microphone that responds to sound waves emanating from the vibrating acoustic cymbal is used, acoustic feedback and acoustic crosstalk from other instruments and ambient noise that is within range of the microphone become problematic, particularly for musical performances that are conducted at elevated sound volume levels.
A microphone is a specific example of a transducer, which in general is a device that is operative to convert an input signal or stimulus in one form into a corresponding output signal or response in another form. In the case of the microphone, the input signal is air pressure waves (sound), and the output signal is an electrical response signal.
An inexpensive and commonly-available microphone is the electret condenser microphone. Referring to prior art FIG. 1A, the principle components of an electret condenser microphone are a housing 4, a very thin and flexible metallized diaphragm 6, and an electret 10, mounted to a metal back plate 9. The diaphragm 6 forms an airtight seal between the air in cavity 8 and external air with which it is in communication via holes (not shown) in the housing. Air pressure differences (sound) cause the diaphragm 6 to flex, changing the distance between it and the back plate 9, which in turn changes the electrical capacitance between them. This capacitance change can be converted to a useful signal using electronics 11 for subsequent processing, amplification, etc. by well-known techniques.
Another type of transducer is an accelerometer. As the name indicates, an accelerometer measures acceleration, serving to convert accelerative forces to proportional electrical signals indicative of acceleration magnitude. Many types of accelerometers have been devised in the past. The majority of these contain a “seismic proof mass” whose tendency to resist changes in its spatial location (that is, its inertia) can be measured in some way. Capacitive accelerometers measure changes in the capacitance of a capacitor whose two plates are attached (directly or indirectly) to a compliantly-suspended proof mass and to a fixed accelerometer housing, respectively. When the accelerometer's housing is accelerated (moved) along the axis of interest, the proof mass tends to remain stationary due to its inertia, and due to its compliant suspension, the distance between the plates changes in proportion to the accelerative force being applied to the housing, thus changing the capacitance between them and providing an indication of the accelerative force.
FIG. 1B shows an electret microphone 30 that has been modified to operate as an accelerometer. In this case, the housing 32 defines a cavity 33 and contains a thin and flexible metallized diaphragm 34, along with an electret 36 mounted to a metal back plate 38. The modification is by way of an added proof mass 40 that is coupled to the diaphragm 34 to provide the necessary increase in inertia for improving sensitivity to accelerative forces. The electronics 42 may or may not be modified as necessary.
The use of accelerometers as musical instrument transducers is known. However, those that are adequate for such applications are expensive and often require time-consuming and non-scalable customization, severely restricting their use. One problem with the use of existing accelerometers is that the proof mass in conventional accelerometers tends to dampen high frequency response, which contains much of the musical information of interest. The problems are compounded in the case of adding a proof mass to an existing electret microphone. The diaphragm of an electret microphone is absolutely diaphanous—thinner and more flexible than an insect wing. The amount of mass to be added would have to be extremely tiny (the diaphragm itself may only be 4 mm in diameter), and its smallness would make the dispensing and application of a consistent amount of adhesive difficult. This in turn would lead to inconsistency in the sound of the assembled transducer.